1. Technical Field
The present invention relates to the manufacture of bead assemblies of the type incorporated into a pneumatic tire. More particularly, the invention relates to a method of manufacturing which enables bead assemblies to be produced automatically with minimum distortion to the green or uncured elastomeric material which forms the bead filler thereby providing a bead with good dimensional uniformity throughout the entire bead assembly, thereby reducing nonuniformity in the final tire into which it is subsequently incorporated.
2. Background Information
One of the components of a pneumatic tire is the bead assembly which consists of an annular bead, usually formed of a wound metal band or cable, which is combined with an elastomeric bead filler usually having a generally triangular configuration. The bead assembly then is formed as part of the final tire and used for maintaining the inflated tire on its mounting rim. It is desirable when producing the bead assembly that it be as free as possible of nonuniform areas and any out of roundness or unwanted projections or depressions, all of which add to the nonuniformity of the final tire in which it is incorporated. Furthermore, it is desirable that the bead assemblies be produced as efficiently and inexpensively as possible in order to decrease the cost of the final tire.
Many known methods for producing tire bead assemblies extrude the bead filler with its final triangular shape, afterwhich it is placed on the bead and secured thereto subsequent to curing. However, during these manufacturing methods it is difficult to handle the uncured green elastomeric bead filler due to its extreme flexibility, without distorting the bead filler. Even minor distortions can cause undesirable nonuniformity in the final tire.
Examples of prior art methods and apparatus for forming tire bead assemblies are shown in the following patents.
U.S. Pat. No. 1,536,080 discloses a very early method of forming a tire bead in which a fabric is coated with a slow curing rubber and encloses a core ring and a filler of faster curing rubber, afterwhich the bead core is semi-cured to a degree which partially vulcanizes the filler and leaves the external coating soft and tacky whereupon the bead core can be incorporated into a tire casing.
U.S. Pat. No. 4,410,389 shows a bead filler assembly apparatus wherein the filler is extruded in a triangular configuration and is placed and attached to the bead.
U.S. Pat. No. 4,662,961 discloses a method of forming a bead assembly in which an elastomeric strip is extruded in order to impart a substantially circular cross-sectional configuration thereto with a square cross-sectional channel formed therein. An adhesive is then applied, afterwhich a wire is wound around the support until the channel is filled to form the final bead assembly.
U.S. Pat. No. 4,933,034 discloses another method of forming a bead assembly in which the bead filler is formed by an extruder and fed onto the bead ring and wound thereabout, and then subsequently bonded to the outer periphery of the bead.
U.S. Pat. No. 4,990,212 discloses a method of forming a bead assembly in which a triangular shaped bead filler is formed and is then wound about the bead ring.
U.S. Pat. No. 5,100,497 discloses another method and apparatus for forming a bead assembly in which the bead filler or apex is extruded in a generally triangular configuration and then wound about the bead ring by a plurality of rollers.
Japanese Patent Application 36-22130 shows a device for assembling metal fabric onto a bead wire without exerting an adverse effect on the strength of the fabric ply. A tubular elastic film is wound around the periphery of the cylinder which can be outwardly expanded. A pair of bell-shaped hoods are mounted around the cylinder containing the elastically flexible film and bead wire whereby the conical portions of the hoods control the expansion of the film when the mounting cylinder is expanded.
Japanese Patent Application 54-57578 and Japanese Utility Model 60-180604 are believed to be the most pertinent prior art with respect to the method of the present invention. Both of these disclosures show the extrusion of a strip of elastomeric material having a pair of wing-like end members which are subsequently folded about a rectangular-shaped bead in order to produce the final bead assembly. However, neither of these prior art Japanese methods are believed to eliminate or materially reduce the unwanted distortions which occur in a green unvulcanized strip of rubber, which is achieved in the present invention disclosed herein. Neither of these methods disclose continuously supporting the unvulcanized green elastomeric material until it has been formed into the final bead assembly, nor do they disclose the incorporation of a reinforcement strip in the bead filler by placement of the strip between the two wing-like end members of the elastomeric strip prior to closure about the bead, nor do they disclose the joined ends of the bead filler strip having a bias angle cut, and the formation of the subsequent splice being performed on a rigid support to further reduce the introduction of unwanted stresses on the uncured elastomeric material as in the method of the present invention.
Therefore, the need exists for an improved method of forming a tire bead assembly which produces a bead assembly with good dimensional uniformity by providing good splice integrity and by providing continuous support for the uncured green elastomeric material which forms the bead filler portion of the bead assembly until it is vulcanized.